Multiple linear actuating cylinder



Nov. 29, 1966 R. M. FISHER 3,288,036

MULTIPLE LINEAR ACTUATING CYLINDER Filed Sept. 12, 1963 FIGURE 4 ROBERT M. FISHER INVENTOR.

FIGURE 8 United States Patent M 3,288,036 MULTIPLE LINEAR ACTUA'ITNG CYLINDER Robert M. Fisher, 20966 Las Flores Mesa Drive, Malibu, Calif. Filed Sept. 12, 1963, Ser. No. 308,529 3 Claims. (Cl. 92-62) This invention relates to piston actuating cylinders and i more particularly to a novel in-line array of actuating cylinders the elements of which may be added together to increase the resultant actuating pressure without an increase in the cross-sectional diametral area of the piston rod elements.

A particular feature of the invention is the incorporation of three types of unit elements which can be assembled in-line in various combinations or which can be used individually. The number of the unit elements of the invention which can be added together is limited only by Eulers formula for long columns which establishes the buckling limit.

Each of the elements of the invention when added to another, or group of preceding elements in the linear column increases the linear output pressure capability of the actuator formed thereby in response to an applied pressure by a factor of between .8 and .9 times per unit added.

This may be expressed as:

1 i( i 2) where F =linear force in pounds per square inch (output);

P =input pressure in pounds per square inch (p.s.i.);

A =area of piston on which input pressure is applied;

A =area of piston applying pressure to load or succeeding elements;

k=increase factor provided by each added element; and

n=number of elements in the linear multiple actuator assembly.

The three types of elements which can be combined in the practise of this invention are a front or forward section, a middle section, and a rear or end section.

If only two elements of the invention are used to form a linear actuator assembly in one form of use of the invention a forward and a rear section are assembled together in line on a common axis. If more than two elements are used together in a linear actuating cylinder as conceived in this invention, then one or more middle sections are inserted between the front and rear sections to make up the multiple piston actuating cylinder.

The front section is threaded at its input end only and the end section at its output end only so that the front and end sections may be fitted together to form a unitary linear actuator. The threads in one are internal and in the other external so that the ends which are threaded may be mated together. A middle section is threaded at either end, one end to mate with end sections or the opposite end of other middle sections and the other end to mate with forward sections or the opposite end of other middle sections.

It is accordingly a principal object of this invention to provide a multiple piston linear actuating cylinder comprising a number of sections'through which the linear force applied at the input end thereof is multiplied by a factor times the number of sections assembled together in line to produce a corresponding increase in the linear output force without an increase in the cross-sectional area of the piston employed.

This and other objects of the invention will become more clear from the specification which follows taken together with the appended claims in view of the accompanying drawings in which:

FIGURE 1 is a drawing partially in crosssection show- Patented Nov. 29, 1966 ing an assembly of one of each of the piston actuator elements of this invention in a linear actuator in one of the forms in which the invention may be used;

FIGURE 2 is a typical front or forward section, according to the invention;

FIGURE 3 is a typical middle section according to the invention;

FIGURE 4 is a typical end or rear section according to the invention;

FIGURE 5 is a representative unitary cylinder assembly embodying another form of the use of the invention;

FIGURE 6 is a cross-section through 6-6 of FIG- URE 1;

FIGURE 7 is a cross-section through 77 of FIG- URE 1; and

FIGURE 8 is a cross-section through 8-8 of FIG- URE 1.

Referring now to FIGURE 1 there may be seen in partial cross section an assembly of the multiple piston linear actuator elements as used in one embodiment of the invention. The individual elements are shown in FIG- URES 2, 3 and 4.

A piston assembly 10 includes piston rod 11 and piston head 12 and is assembled into a cylindrical body 13. Body 13 is the type used for a forward section according to the invention, and is threaded at the output end 14 thereof with external threads. Within body 13 at the input end 15; thereof a cap 16 is fitted tightly. Cap 16 may either be threaded on its outer circumference with appropriate matching threads provided in the inner top surface of the body wall of body 13 or cap 16 may be press-fitted into body 13 tightly sealed thereby against the inner walls 22 and retained by ring 17 in groove 18 provided therefor and held down by a ring 33.

Alternatively, cap 16 may be machined as an integral:

part of cylinder body 13 forming a unitary end piece. In any event cap 16 has a central aperture or bore 19 to receive piston rod 11 slidably but tightly therein. An O-ring 21 is fitted in bore 19 in a rectangular groove 20 therein to seal piston rod 11 against outside pressure and leakage from within cylinder 13.

The head 12 of piston 10 is provided with a rectangular groove 23 about the periphery 24 thereof to receive another O-ring 25 to seal piston head 12 off from outside pressure.

Piston head 12 and rod 11 forming piston assembly 10 can be seen to be an integral solid structure. In cylinder wall 22 two relief or intake ports 26 and 27 are provided. Relief port 26 is provided to permit exhaust of pressure from the space 28 above head 12 on extension of piston 10. Extension is movement of the piston in the direction of piston rod 11. Retraction is movement in the direction of head 12 into the cylinder. Pressure is normally applied to move rod 11 in the direction away from its associated piston head 12.

Intake port 27 is the principal pressure port 27 which acts as an intake for fluid from external sources port during extension of piston 10 while, as above described, pressure is exhausted through port 26. Port 26, on the other hand can be pressurized by external means to retract rod 10 by acting on the upper surface of head 12. When piston is being retracted in this manner the relief of pressure out of space 29 is through port 27 as will be more clear from the description below when ports 27 and 26 are being used as inlet or relief ports then either ports 51 and 56 or 52 and 57 must be closed off dependent upon Whether extension or retraction is being employed.

At the input end 30 of cylinder 13 a cap 31 similar to cap 16 (when used as a separate element in one of the forms of the invention above described) is inserted against a retaining ring 32, similar to retaining ring 17,

. within the inner wall 22 of cylinder body 13. Lock rings 33 and 34 holds caps 16 and 31 against their respective retaining rings 17 and 32 in cylinder 13.

In cap 31 a bore 35 is provided similar to bore 19 and similarly equipped With an O-ring 36. Bore 35 is provided to receive the piston rods of successive elements connected to cylinder 13 as hereinafter described. Cap 31 is provided with an external O-ring 37 in a groove 38 cut into the periphery thereof.

The components hereinabove described and fitting within cylinder 13 comprise a front or forward unit of the linear actuator of this invention.

The components of a middle section of the invention are incorporated in cylinder section 40 which has an internal thread 41 at the output end thereof and an external thread 42 at the input end thereof. Within cylinder 40 piston assembly 43-44 is inserted. Piston 43-44 is similar in construction to piston element 11-12 except that piston 43-44 has a central aperture 45 therethrough. When cylinder 40 is screwed to cylinder 13 by the mating of threads 14 with threads 41 piston shaft 43 butts against the bottom surface 47 of piston head 12 so that any pressure on piston head 12 due to the application of pressure thereto from external fluid or pneumatic sources at intake port 27 will move piston rod 11 outwardly. Continued application of pressure at inlet 27 results in the passage of the pressure fluid through aperture 45 in rod 43 to fill space 54 and continuing through aperture 45a to fill space 67. Pressure is thus applied both to piston head 44 and 44a, the former causing rod 43 to butt against head 12 and the latter to cause rod 43a to butt against head 44, the respective pressures adding according to the formula F given below. In the input end of cylinder 40 a cap 31a is provided which matches in every respect cap 31 and is held in place by stop rings 32a and 34a, and includes inner and outer O-rings 36a and 37a and the central bore 35a to receive the piston rod from a subsequent middle section or from a rear or end section. The cylinder wall 40 of the middle section unit includes a relief port 51 which permits exhaust of pressure from the space 53 on extension of piston assembly 43-44 and alternate exhaust or pressure port 52 is similar to port 27 in its function and which permits intake of pressure from external sources if port 52 is to be used as the inlet port whereupon ports 27 and 57 must be closed off.

The components cap 31a and its associated stop rings 32a, 34a and O-rings 36a, 37a and piston 43-44 within cylinder body section 40 comprise a middle section of the elements of this invention. When a middle section assembled in cylinder. body 40 is screwed by means of its inside threaded end 41 to the outside threaded end 14 of cylinder body section 13, rod 43 of piston 43-44 is tightly fitted in bore 35 of end cap 31 of the front section and butts against the end 47 of the head 12 of piston rod in the upper or front section.

The end or rear section unit of the invention is contained in a cylinder body 55 having apertures 56 and 57 which function in the same manner as similar apertures 26, 27 and 51, 52 in the front and middle sections, respectively. Cylinder body 55 is closed off at the bottom by bottom end cap 58 which has a rectangular groove 59 to accommodate an O-ring 60.

End cap 58 may be machined as an integral part of body 55 in the same manner as cap 16 may be an integral machined part of body 13 previously described. End cap 58, when a separate part, is held in place by stop rings 61 and 62. O-ring 60 forms a seal against outside pressure. Within body section 55 a piston assembly 43a-44a is fitted, which corresponds exactly to piston 43- 44 in the middle section. The output end 63 of the bottom section of cylinder body 55 is threaded internally to mate with the external threaded portion 42 of cylinder body 40 of the middle section. When end section 55 is assembled to middle section 40 the piston rod 43a of end section 55 butts against the bottom 66 of piston head 44.

It may be seen therefore that three sections, respectively, in cylinder bodies 13, 40 and 55 may be assembled together to form a multiple linear actuating cylinder.

The outside threaded end 14 of cylinder body 13 may sections 40 may be interposed end to end between a front section 13 and an end section 55 to provide a multiple element actuator according to this invention wherein a total of 4 or more sections are employed. The limit is only that which may be computed from Eulers formula for long columns which may be found in any text on strength of materials. One such reference is on p. 465 in the Mechanical Engineers Handbook, Fifth Edition, edited by Lionel S. Marks and published by McGraw-Hill Book Co., New York, 1951.

When a typical assembly such as that illustrated in FIGURE 1 is made and incorporates a front section 13, a middle section 40 and an end section 55, for a piston head cross-sectional area (of piston heads 12, 44 and 44a) of one square inch and a piston rod cross-sectional area (of piston rods 10, 43 and 43a) of one-tenth square inch, the total pressure applied by end cap 10 will be 2.8x the applied pressure for an applied pressure of one unit of pressure on piston head 12 from pressure at inlet 27, inlets 52 and 57 being closed off.

This is computed on the basis of the following formula:

a= 1 2) Where F force area A =piston area A =piston rod area n=total number of sections In the example given F may properly be called the multiplication factor or enhancement factor.

If more middle sections are added as, for example,

there were three middle sections and a front and an end section, the total pressure applied by end 65 of the linear actuator will be based on the factor N 1 or 1+(5-1) (l,00.1) times the applied pressure or, 4.6 times, the pressure applied to piston rod 10.

It may be further seen that the same piston assembly 43 -44 '(43a44a) may 'be used in both middle and end sections. It may also be seen that the same end caps 31 or 31a may be used in front and middle sections so that considerable economy of assembly is possible in the manufacture and exploitation of multiple sectional linear actuator assembles according to this invention.

The individual components which are stocked would include .the following:

From the asterisked items it may be seen that six of the components are used individually and the remainder may be used alternatively in different elements as needed. If cap elements 16, 31 and 31a should be integral with It should also. be clear to those skilled in this art that additional middle their respective cylinders the end stop rings, of course, would not be required.

As a further extension of the use of the invention there is illustrated in FIGURE 5 an assembly of elements such as shown in FIGURE 1. The elements 13, 40 and 55 of FIGURE 1 however are formed as a single cylinder 76 into which the various pistons, centering rings, caps, and so on are dropped to build up a multiple piston actuating cylinder. The internal components of the article illustrated in FIGURE 5 are identical with those illustrated in FIGURE 1 and bear corresponding reference characters. The operation of the article in FIG- URE 5 is the same as above described for that shown in FIGURES 1 through 4.

Cylinders such as 70 are provided in different lengths to accommodate different numbers of linear actuator piston elements in line therein. The same formula for output actuating pressure multiplication applies to the single cylinder assembly of multiple pistons as to the assembly of several screwed together sections.

What is claimed as new is:

1. A linear actuating cylinder comprising:

a plurality of interfitting cylindrical guides; and

a plurality of pistons positioned end-to-end, each of said pistons being assembled in one of said interfitting cylindrical guides, respectively, forming thereby a section; the upper one of said plurality of pistons being solid, the remaining pistons each having a central aperture for pneumatic or fluid flow transfer therethrough;

the bottom of each of said pistons being normally positioned at the top of each succeeding piston whereby the pressure applied to the top most of said pistons is multiplied by a factor between .8 and .9 times the number of said sections assembled together in-line on a common axis.

2. A multiple linear piston actuator assembly comprising:

a first piston element having a piston rod and a piston head, said head being larger in diameter than said rod, said rod and head being an integral solid strucend for end in said housing to form a linear axial assembly, said separation means being interposed between said first and said second, and between said second and said third pistons, respectively, so as to provide a seal for said piston rods while permitting slidable motion of said pistons within said housing in response to pressure applied to said first piston, said pressure being magnified at the third piston thereof due to the series accumulation of force down the axis of the linear actuator assembly.

3. A multiple piston linear actuating assembly comprising a plurality of similar interfitting body sections;

one of said plurality having a solid piston rod and head assembly movable therein;

the others of said plurality having piston and rod assemblies movable therein and said piston and rod assemblies of said others including a central aperture;

the respective piston and rod assemblies of said one and said others being in .alinement on a common axis, the rod of each of said others abuttin the respective pistons above it; and

apertures in each said body sections on either side of said pistons therein, each said body sections havinlg end caps through which the respective rods project and interfit into respective section above, the topmost section having a projection of said rod therein, the bottommost section being closed at the bottom thereof,

whereby pressure applied to one aperture beneath one piston forces piston to move and proceeds through said central apertures to the other pistons, the pressures on the totality of pistons being cumulative in proportion to the product plus one of their number less 1 and the dillerence between the diameters of said rods and pistons.

References Cited by the Examiner UNITED STATES PATENTS 825,866 7/1906 Rogers 91-411 X ture;

a second piston element including a piston rod and a piston head identical in external configuration to said first piston element and having a central aperture axially therethroulgh;

at least a third .piston element similar to said second piston element; apertured separation means; and

a cylindrical housing being solidly capped at the bottom end thereof and having an apertured cap for closing the top thereof;

said first, second and third pistons being assembled,

MARTIN P. SCHWADRON, Primary Examiner.

RICHARD B. WILKINSON, SAMUEL LEVINE,

Examiners.

H. G. SHIELDS, Assistant Examiner. 

1. A LINEAR ACTUATING CYLINDER COMPRISING: A PLURALITY OF INTERFITTING CYLINDRICAL GUIDES; AND A PLURALITY OF PISTONS POSITIONED END-TO-END, EACH OF SAID PISTONS BEING ASSEMBLED IN ONE OF SAID INTERFITTING CYLINDRICAL GUIDES, RESPECTIVELY, FORMING THEREBY A SECTION; THE UPPER ONE OF SAID PLURALITY OF PISTONS BEING SOLID, THE REMAINING PISTONS EACH HAVING A CENTRAL APERTURE FOR PNEUMATIC OR FLUID FLOW TRANSFER THERETHROUGH; THE BOTTOM OF EACH OF SAID PISTONS BEING NORMALLY POSITIONED AT THE TOP OF SAID SUCCEEDING PISTON WHEREBY THE PRESSURE APPLIED TO THE TOP MOST OF SAID PISTONS IS MULTIPLIED BY A FACTOR BETWEEN .8 AND .9 TIMES THE NUMBER OF SAID SECTIONS ASSEMBLED TOGETHER IN-LINE ON A COMMON AXIS. 